Coffer

• (architecture) A coffer, in architecture, is a sunken panel in the shape of a square, rectangle, or octagon that serves as a decorative device, usually in a ceiling or vault. Also called caissons, or lacunar.
• (geology)

1. A rectangular plank frame, used in timbering levels. Also spelled cofer.
2. A floating dock; a caisson. Standard, 2
   Source: Dictionary of Mining, Mineral, and Related Terms